FLOATING ROOF TANK

A Floating Roof as its name implies, actually floats on the surface of the liquid in the tank. As the liquid level changes the roof is designed to move up and down with the liquid level - i.e. Filling, Emptying, Expansion and Contraction due to temperature changes. This type of tank roof minimizes the vapor space between it and the liquid surface. Since there is no large vapor space for the liquid to evaporate into, vapor losses are also minimized
In its simplest form, the floating roof is merely a large, disc, slightly smaller in diameter than the tank shell. It is fitted with a system of flexible 'shoes' to close the space between the edge of the roof and the tank shell in order to minimize vapor loss

In modern usage, there are two main designs of floating roof
The 'Pontoon' roof
The 'Double-Deck' roof